A sequential extraction procedure to evaluate the mobilization behavior of rare earth elements in soils and tailings materials

A novel sequential extraction method for evaluation of the mobilization behavior of rare earth elements in soils and mine tailings materials is presented. The sequence consists of the following four steps: 0.05 mol L-1 calcium nitrate (easily soluble and ion exchange fraction), 0.1 mol L-1 citric acid (fraction mobilized by complexation and carbonate bound), 0.05 mol L-1 hydroxylamine hydrochloride (pH = 2) (reducible fraction), 1.4 mol L-1 nitric acid (acid soluble fraction). The procedure was optimized with a certified soil material and a mine tailings material and was applied to eight samples of a soil profile. The different results obtained by using either the developed method or the widespread used BCR-Method for comparison are discussed. There were clear advantages using the newly created sequential extraction procedure in getting more detailed information about the bioavailable fraction and a fraction addressing REE phosphates. (C) 2015 Elsevier Ltd. All rights reserved.